A paralysis field, also known as a neural field, was a technological device utilized by the Kelvans to neutralize the nerve impulses to an individual's voluntary muscles. The beam was emitted from a paralysis projector worn on the user's belt.
Rojan used the paralysis field against Captain Kirk and his landing party from the USS Enterprise to ensure cooperation. After the Kelvans took over the Enterprise, Kirk and the remaining crewmembers attempted to find ways to counteract the field's effects. (TOS: "By Any Other Name")